Main aide to cleric blamed for a failed military coup attempt has been detained, after Gulen's nephew is also held.

Turkish authorities detained on Saturday a key aide to Fethullah Gulen, the US-based Muslim cleric Turkey blames for a failed military coup attempt.

Halis Hanci, described as Gulen's right-hand man, apparently entered Turkey two days before the abortive coup, a presidency official told reporters.

Earlier on Saturday, Turkish authorities also detained a nephew of Gulen in connection to the coup attempt, the Anadolu state news agency reported.

Muhammed Sait Gulen was detained in the northeastern city of Erzurum and will be brought to the capital Ankara for questioning.

Among possible charges that could be brought against him is membership of a "terrorist" organisation, the agency said, adding that he was also wanted over the leak of questions from the 2010 civil service exams.

It is the first time a relative of Gulen has been reported detained since the July 15 events. In May this year, another nephew of the former imam in self-imposed exile was detained in connection with schools run by the movement, according to a state media report at the time.

Pennsylvania-based Gulen is accused of "masterminding" the July 15 attempt to topple the government of President Recep Tayyip Erdogan through his movement - a claim he strongly denies. Turkey is seeking Gulen's extradition from the US.

Widening purge

Turkey has detained over 13,000 people as part of a crackdown in response to a failed military coup, President Recep Tayyip Erdogan said late Saturday, not long after the presidential guard became the latest target of the purge.

Of those detained, 6,000 have been placed under arrest.

Some 37,500 civil servants and police officers have so far been suspended, including many from the education ministry.

The rapid pace of arrests since the coup attempt has worried many of Turkey's Western allies, who say they see the country going down an increasingly authoritarian road.